There are two main types of artificial teeth, namely crowns and denture teeth. Crowns are designed to fit a root stump which is left in the gum after the whole top part of the tooth has been removed, while denture teeth are intended to replace teeth which are no longer present. Denture teeth are usually attached to a bridge which extends between two teeth or to a plate which is worn against the upper or lower palate.
Crown teeth or crowns must be custom made because they must correspond at least approximately in shape to the teeth that they replace, and must fit whatever shape of stump is left for the attachment. Historically, crowns have been cast from a suitable metal which is left in its original color, so that the contrast with the natural teeth make them quite obvious. A more cosmetically acceptable crown is molded from ceramic material and then surface painted to match the surrounding teeth as closely as possible. Such crowns and the process by which they are made have a number of disadvantages. For example the process is very labour intensive and the painted-on color wears off in time. In addition, the ceramic materials from which these crowns are made are harder than natural teeth and this often results in accelerated wear of the opposing teeth. Finally, even with careful workmanship it is difficult to make the appearance of a painted tooth match that of the adjacent real teeth. Teeth are made up of three major layers, namely an interior pulp, a surrounding dentine, and an outer coating of enamel; the enamel and dentine are translucent so that all three layers contribute to the color which is visible from outside the tooth. The resulting depth and distribution of color in a natural tooth is very difficult to duplicate.
A new crown making technology which has recently become available provides a tooth body made from synthetic material, usually plastics, material which is shaped in a computer- controlled milling machine and then surface painted. The process is highly automated and provides great savings in labour, while another benefit is that the hardness of these teeth can be matched more closely to that of natural teeth. The problems of surface wear of the painted-on color and the less natural look of a painted-on surface are still present.
Denture teeth generally are not custom made, but instead are provided in a wide assortment of standard shapes, sizes and colors, from which the denture maker may choose. At one time most denture teeth were molded from homogeneous blocks of ceramic and surface painted in a manner similar to that described above for crown tooth manufacture. Current technology provides denture teeth which are molded with a number of internal successive colored layers, each of the layers contributing to the color which is visible on the outside of the tooth. This molding process provides a tooth with a depth and distribution of color more closely resembling that of a natural tooth, but requires at least three separate molds for each tooth and would be prohibitivly expensive in a custom process for producing individual crowns.